Maintaining well integrity during well life cycle plays a significant role in the life of a well. Sustained casing pressure (SCP) or Sustained annulus pressure (SAP) in oil and gas wells can result in leakage of the well fluid in undesired regions of the well. Failure to control or manage Annuli pressure may result in uncontrolled release of high-pressure hydrocarbon fluids from formation to the surface thereby leading to significant safety issues and environmental damage.

The Exploratory Well A of Oil India Limited, in the western Block of the Baghjan Structure, was drilled to a measured depth of 4485 m as a J-Bend well and was completed in 4462-m Langpar Sand through perforation in the range 4462.0 m – 4464.0 m in May 2016 after completion with permanent packer. After few days of production testing gradual increase of pressure in the B annulus was observed although there was not any pressure at A- annulus indicating communication behind B annulus casing. Moreover sand, silt, stones and pebbles up to the size of 1.5 cm along with well fluid was observed at the control head. Subsequently, caving level was checked and found at 15 m from surface. Placing adequate well barriers to mitigate sustained annulus pressure became extremely challenging as killing methods viz circulation, bull-heading etc. did not show any encouraging results. CTU operation for wellbore cleaning/ killing was a no-no with available resources for the sizes of stone/pebbles in the bore. Owing to various well integrity issues it was decided to plug and abandon the well, however, with alternate methodology/approach as conventional methods won't yield.

This paper discusses the details of workflow, design, surface arrangement, fluid selection, well control method deployed to subdue the well and subsequent successful abandonment of the well, mitigating sustained annulus pressure issue in a cost effective manner. The abandonment plan was designed on the basis of uncertainties in sub surface well condition, hazard identification, environmental impact and regulatory requirement. This paper also details the different approaches adopted for P&A and step by step plan vis-à-vis actual scenario combined with calculated risks encountered during the execution phase.

As drilling and completion of exploratory wells are expensive, it is critical to identify any well integrity issues and place adequate well barriers in the most-suitable manner to ensure environmental protection as per regulatory requirement. We addressed this, through a customized workflow for design and placement of well barriers eliminating sustain annulus pressure and subsequent successful plug and abandonment using the available cost effective resources.

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